Eocene

Eocene is the second geological epoch of the Cenozoic era. It extended from the end of the Paleocene epoch, about 54 million years ago, to the beginning of the Oligocene epoch, about 34 million years ago. The oldest known fossils of most of the modern orders of mammals appear
within a short space of time during the Early Eocene, including the ancestors
of camels, horses (notably Hyracotherium), rodents,
bats, and monkeys; also evident are members of modern plant genera, including
beeches, walnuts, and elms. The world climate was warmer than at the present
time.